Effects of dietary sulfur source on rumen pH and hydrogen sulfide gas concentration

Abstract

A variety of sources of S have been utilized to study S toxicity in cattle; however, it is unknown if these S sources have similar potential to produce ruminal hydrogen sulfide (H2S). The objective of this study was to evaluate the effects of different sources of dietary S commonly used in ruminant S toxicity research on ruminal pH and gas-cap H2S. Five cannulated steers were used in a 5×5 Latin square and fed 1 of 5 diets containing 0.49% S once daily at 1.3% of body weight (DM basis). Dietary S sources included ethanol co-products: dried distillers grains plus solubles (DDGS), condensed corn distillers solubles (CCDS), or inorganic sources: sulfuric acid (SA), sodium sulfate (SS), and calcium sulfate (CS). All diets contained 45% corn and 10% grass hay (DM basis). In the DDGS treatment, DDGS was included at 42% diet DM and contributed 0.40% S. In the non-DDGS treatments, DDGS was included at 21% diet DM and contributed 0.19% S to these diets. In the CCDS treatment, CCDS was included at 7% diet DM and contributed 0.19% S to the diet. For the inorganic treatments (SA, SS and CS) S sources contributed 0.17% S to the diet. In the non-DDGS diets, soyhulls were included to make up the balance of diet DM (15% diet DM for CCDS diet and 21% diet DM for the inorganic S source diets). Sampling of ruminal pH and H2S gas concentration occurred at 6h post-feeding. Diet pH (P<0.01; SEM±0.032) differed due to S source, with SA (3.93) having the lowest pH (P<0.01) whereas SS (4.79) and CS (4.79) were greatest (P<0.01), but did not differ (P=0.97). The co-product diets were intermediate, with DDGS (4.08) having a lower (P<0.01) pH than CCDS (4.18). However, ruminal pH at 6h post-feeding (SEM±0.076) was least (P<0.01) for CS (5.03), followed by SA (5.28) which was lesser (P≤0.05) than DDGS (5.40), SS (5.43), and CCDS (5.50) which did not differ (P≥0.09). There was no difference in S intake (P=0.31) or ruminal H2S concentration (P=0.62) among treatments. Even though dietary pH varied among treatments ruminal pH differences were minimal and no differences in ruminal H2S were observed, suggesting that results of experiments utilizing these different S sources to research S toxicity may be comparable.